Coupled multielectrode array sensors (CMAS) (see U.S. Pat. No. 6,683,463, U.S. Pat. No. 6,132,593, and U.S. Pat. No. 7,180,309) and other electrochemical sensors for corrosion monitoring are subject to the bridging effect of the formation of electron conducting deposits that causes the short-circuiting among the sensing electrodes [see S. Papavinasam, “Electrochemical Techniques for Corrosion Monitoring,” in “Corrosion Monitoring Techniques,” Lietai Yang, ed., Woodhead Publishing, Cambridge, UK (2008), pages 77-79]. These electron conducting deposits may be formed by the corrosion of iron in an environment containing hydrogen sulfide (H2S), because the corrosion products (such as FeS) are semiconductor materials. When the sensing electrodes are short-circuited, the corrosion current cannot be accurately derived by the current that is measured by the sensor instrument. Thus, the sensor instrument cannot effectively measure the corrosion rate. A CMAS probe with coated, fingered electrodes has been described for use in liquid systems containing hydrogen sulfide to avoid the bridging among the neighboring electrodes (see U.S. Pat. No. 8,298,390). In the probe with coated, fingered electrodes, the active sensing surface area of each electrode is physically separated from the sensing areas of neighboring electrodes by a long, coated surface. Such a long, coated surface makes it difficult to form a continuous layer of an electron conducting path among neighboring electrodes' sensing areas. However, such probes cannot be used in a system that cannot form an ion conducting path among the neighboring electrodes' sensing areas. Examples of such systems are untreated natural gases and oil-water mixtures that contain hydrogen sulphide. CMAS probes with closely packed electrodes on a small surface area have been used in oil-water mixtures (see Yang, et al 2005) and simulated natural gas systems (see Sridhar et al, 2006) that did not contain hydrogen sulphide. In the CMAS probes with closely packed electrodes on a small surface area, the sensing area of one electrode is close to the sensing areas of the neighboring electrodes and the ion conducting path can be easily formed by a layer of water adsorbed on the surface between the sensing area of one electrode and the sensing areas of other electrodes. This is in the case of natural gas when the humidity is above a certain point that would cause corrosion. The ion conducting path can also be easily formed by small sized water particulates in the case of oil-water mixtures. However, the probe surface where the sensing areas are can be easily covered by a layer of electron conducting deposits and such a closely packed CMAS probe is subject to the bridging effect.
This invention is related to a CMAS probe that has coated, fingered electrodes and has a mechanism to maintain the ion conducting path among the active sensing areas of the electrodes that are physically separated to avoid the formation of a continuous layer of electron conducting deposits along the path between any pairs of the electrodes.